This invention relates to a process for removing tobacco stems from tobacco leaves. More specifically, the present invention pertains to a process which reduces the percentages of fines in the separating of stems and lamina of tobacco leaves.
In the processing of tobacco it is necessary to remove the stems and veins from the lamina portion of the leaves in the manufacturing of smoking tobacco products. The stems and veins have undesirable burning qualities, particularly in the harshness of taste and therefore whole tobacco leaf is processed to separate the stems and veins from the lamina in order to remove their undesirable properties if they are to be used in tobacco products. Therefore, in the preparation of tobacco leaf material for use in smoking articles, it is customary to subject these tobacco leaves to a threshing operation to separate the stems and veins from the remaining portions of the leaf early in the tobacco processing for use in smoking articles. Since the remaining portion of the leaf, the lamina, is the portion of the tobacco leaf that is most desirable in the making of smoking products, in the separation of the lamina from the stems it is desirable to keep the lamina in relatively large pieces as the large pieces may be handled and shredded more easily during processing into tobacco filler for smoking articles. Moreover, in the de-stemming processing, it is important to keep the production of fines, the dust-like particles of lamina, to a minimum as the fines, unless processed further into reconstituted tobacco sheets, are not suitable for use in tobacco products. Thus, production of large amounts of fines represents a significant loss of tobacco lamina.
The stems, after separation, are further processed to remove the undesirable properties of the stems and the processed stem is then used in other smoking products. For example, these stems may be ground and used in a reconstituted tobacco product which makes for a synthetic leaf that may then be blended back in with other processed leaf portions and used in a tobacco blend for a smoking article.
In known tobacco leaf de-stemming processes, the leaf stems are separated from the leaf lamina by first subjecting the leaves to a mechanical threshing action of sufficient duration and intensity to completely detach the lamina from the stems. The resulting stem-lamina mixture is then subjected to a classification step. In typical threshers, lamina is separated from stems or veins by the action of one or more toothed rotors beating against stationary teeth, or by the action of counter-rotating toothed rotors, or by the action of a toothed rotor beating against a perforated cage or basket or by the action of a toothed rotor beating first against stationary teeth and then against a perforated cage or basket. Because of the relatively ductile nature of the tobacco lamina, it will not easily break away from the stems. Therefore, multiple impacts by the rotors are required to tear and rip the lamina from the stem.
The threshing processes currently in use, even when carefully controlled, result in a production of a preponderance of small pieces of lamina. Moreover, an unacceptable amount of tobacco fines is produced because of the pulverizing action of the toothed rotors and the multiple impacts required to completely detach all of the lamina.
It is an object of the present invention to provide a process to increase separation of stem and lamina and for reducing the amount of fines from the de-stemming of a tobacco leaf.
It is a further object of the present invention to provide a process for treating tobacco leaves, prior to de-stemming, with a humectant.
It has been found that with the addition of a humectant to whole tobacco leaf prior to the de-stemming operation, the amount of lamina fines produced in the de-stemming operation is sufficiently improved over present commercially acceptable processes for de-stemming.
Particularly, the present invention provides a process for treating and processing whole leaf tobacco comprising the steps of adding a humectant to whole tobacco leaf; separating stems from lamina of the tobacco containing the humectant; and, transferring the treated lamina to storage.
It has been found that by applying humectant(s), particularly glycerin in a concentration of from 0.5% by weight to 1.5% by weight of the whole leaf tobacco prior to the first de-stemming or threshing stage significantly reduces both total and objectionable stem content of the lamina in present commercially available equipment under existing operating conditions with no increase in tobacco degradation.